Oxygen reduction in 0.5M H2SO4 has been investigated at Pt0.65Cr0.35 , Pt0.2Cr0.8 and at surfaces produced from them by selective dissolution of the Cr component. Rotating disk electrodes (RDE) were used to examine the oxygen reduction reaction (ORR). The published (1–2) surface analysis using x‐ray photoelectron spectroscopy (XPS) combined with sputter profiling and Rutherford backscattering spectrometry (RBS) convincingly demonstrated that the surface region can be selectively depleted of the Cr component by electrochemical excursions to potentials positive of ∼+1.25V vs. RHE. For the more Cr‐rich alloy very severe depletion (>500Å) occurs upon prolonged potential excursions above +1.25V. For the Pt0.65Cr0.35 sample, the surface depletion extends about 2–3 monolayers into the surface. Electrochemical characterization by cyclic voltammetry also confirms that the surface becomes progressively roughened as the potential exceeds the region where chromium is passive. Extensive roughening of the Pt0.2Cr0.8 surface results in a significant increase of the measured ORR current per geometric area of the RDE. Tafel slopes of the ORR for moderately rough surfaces (roughness factor, R≤5 ), produced from either starting alloy, are nearly identical to pure smooth Pt. For rougher surfaces (produced only at the more Cr‐rich starting alloy) the Tafel slopes determined from a mass‐transfer corrected plot of logfalse[jnormaldfalse(jR−1false)/jnormald−jfalse]normalvs.Enormalapp are also nearly identical to those obtained at smooth Pt. It is concluded that the measured increase of ORR current following the roughening of the RDE alloy electrode is due solely to the increase of Pt surface area. The mechanistic and practical implications of this effect in fuel cell electrochemistry are discussed.

The surface microstructures of c-axis-oriented films of YBa(2)Cu(3)O(7), deposited by off-axis magnetron sputtering on MgO and SrTiO(3) single crystal (100) substrates, have been investigated with scanning tunneling microscopy and atomic force microscopy. There is strong evidence that the films nucleate as islands and grow by adding material to the edge of a spirally rising step. This results in columnar grains, each of which contains a screw dislocation at its center. This microstructure may be of significance in determining superconducting properties such as critical current, and represents a significant difference between thin films (especially those grown in situ) and bulk materials.

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